Include preferred labels / descriptions for entities in JS on EntityView

EntityView now initializes a fallback chain for current context, and in
experimental mode, wbUsedEntities and wbEntity include data with fallback
using this chain, to have data to be viewed by final user included.

Change-Id: Ic8ad24f49ba7fafe11e3dceb5d36e18d5b9ef19f
Merge "Include preferred labels / descriptions for entities in JS on EntityView"